As supplies of the glasses run short, some customers are turning to knockoffs that don't offer the protection from damage that the space event can cause. The real glasses have very dark lenses, designed for viewing the space event.

The knockoffs often don't meet industry standards, according to the American Astronomical Society (AAS) and NASA, which have put out a list of brands that are deemed safe.

"It's a bunch of unscrupulous people cashing in on the eclipse and putting public safety at risk," Richard Fienberg, press officer for the American Astronomical Society (AAS), told Reuters.

Amazon said in a statement on August 13 it is contacting customers that may have bought knockoff glasses from the site and is offering refund "out of an abundance of caution." The statement notes that all eclipse glasses sold on the website are required to comply with the industry standards for safety. The company also removed some listings for glasses, but did not specify which brands.

To make sure that the glasses you're planning on using or buying complies with the standards set out by the organizations, check if they're one of the approved brands below. The AAS also stated not to pay much attention to the ISO seal stamp meant to authenticate the glasses as real, as some knockoffs have the stamp as well.